Over three million children undergo anesthesia and surgery in the United States. It is reported that 50 to 75 percent of these children develop significant behavioral stress prior to their surgery. In adults, preoperative behavioral stress has been shown to correlate with postoperative clinical outcomes such as pain and analgesic requirements, and prolonged recovery and hospital stay. In children, however, the only data available links preoperative behavioral stress to postoperative behavioral changes such as night-mares and apathy and withdrawal. Multiple interventions have been suggested to treat preoperative behavioral stress in children. Unfortunately, currently there is a trend towards reduction in preoperative interventions aimed at children. This is not surprising considering the present medical-economic climate and the absence of postoperative clinical outcome data documenting the link between behavioral stress prior to surgery and postoperative clinical recovery in children. The primary aim of this project is to develop and validate a model describing the link between stress reactivity, preoperative behavioral stress and postoperative recovery as assessed by convergent clinical, neuroendocrinological, immunological, and behavioral measures. As secondary aims (1) we will examine the pattern and consistency of these relations across various age groups (2) we will determine the relationship between the clinical, behavioral, neuroendocrinological and immunological components of the perioperative stress response. and (3) we will determine the effect of child-parent interaction on the perioperative stress response. This will be accomplished using a natural history, longitudinal study design. This proposal represents an ongoing unique interdisciplinary collaboration between a pediatric anesthesiologist who routinely encounters perioperative behavioral stress in children, a developmentalist who has the knowledge and expertise to evaluate such a complex phenomenon, and a neuroendocrinologist who has extensively studied hormonal and immunological aspects of the human stress response. The broad, long term objectives of this research are the evaluation, development and implementation of preoperative interventions so that preoperative behavioral stress in children can be treated effectively.